Cleft lip with or without cleft palate (CLqP) is one of the most common birth defects. The results of previous linkage studies of CLqP have been inconclusive and contradictory. No linkage analysis has been performed using complex models of the disease in the analysis. We propose to perform an analysis of CLqP to determine the most appropriate mode of inheritance, assuming one major gene and other multifactorial components, on a set of 38 multiplex families with CLqP using a new method to allow for multiplex ascertainment, and then use that mode of inheritance to perform linkage analysis on these same families. [unreadable]